1. Field of the Invention
An aspect of the present invention relates to an electric tool having air inlets and air outlets that supply and discharge cooling air for cooling an electric motor serving as a drive source and that are formed in a housing.
2. Description of the Related Art
FIG. 12 shows the configuration of an impact driver as an example of the electric tool.
FIG. 12 is a side cross-sectional view of the impact driver. An illustrated impact driver 1 is a tool that drives a rotary impacting mechanism while taking a battery 2 as a power source and an electric motor 3 as a drive source and imparts rotation and a strike to an anvil 4, to thus intermittently transmit rotary striking force to an unillustrated tip tool and drive a screw into a material to be fastened.
The electric motor 3 is housed in a body 5A of a housing 5, and both ends of an output shaft 6 (a motor spindle) of the motor are supported by ball bearings 7 and 8 in a rotatable manner. A cooling fan 9 is tied to the output shaft 6. A switch 10 that toggles on and off a power supply from the battery 2 to the electric motor 3, to thus activate and deactivate the electric motor 3, is provided in an upper portion of a handle 5B of the housing 5.
In the rotary impacting mechanism built in a hammer case 11, rotation of the output shaft 6 of the electric motor 3 is decelerated by way of a planetary gear mechanism 12 and transmitted to a spindle 13, whereupon the spindle 13 is rotationally driven at a given velocity. The spindle 13 and the hammer 14 are joined together by means of a cam mechanism. The cam mechanism is made up of V-shaped spindle cam grooves 13a formed in an outer peripheral surface of the spindle 13; V-shaped hammer cam grooves 14a formed in an inner peripheral surface of the hammer 14; and balls 15 engaging with the cam grooves 13a and 14a. 
The hammer 14 is urged toward a tip end (i.e., in a rightward direction in FIG. 12) at all times by means of a spring 16. When remained stationary, the hammer is situated at a position spaced apart from an end face of the anvil 4 by means of engagement of the balls 15 with the cam grooves 13a and 14a. Unillustrated protuberances are symmetrically formed at two positions on each of mutually-opposing rotational planes of the hammer 14 and the anvil 4.
When the spindle 13 is rotationally driven as mentioned previously, rotation is transmitted to the hammer 14 by way of the cam mechanism. Before the hammer 14 makes half rotation, the protuberances of the hammer 14 engage with the protuberances of the anvil 4, thereby starting rotation of the anvil 4. Because of reaction force resultant from engagement, relative rotation arises between the hammer 14 and the spindle 13, whereupon the hammer 14 starts receding toward the electric motor 3 along the spindle cam groove 13a of the cam mechanism while compressing the spring 16.
When the protuberances of the hammer 14 get over the protuberances of the anvil 4 as a result of receding action of the hammer 14, to thus become disengaged from each other, the hammer 14 is moved forwardly by urging force of the spring 16 while being rapidly accelerated in the rotating and forward directions by means of elastic energy accumulated in the spring 16 and action of the cam mechanism as well as rotational force of the spindle 13. The protuberances are again engaged with the protuberances of the anvil 4, to thus initiate rotation in an integrated fashion. At this time, strong rotational striking force is exerted on the anvil 4, and hence rotational striking force is transmitted to the screw by way of a tip tool attached to the anvil 4.
Subsequently, similar operation is iterated, whereby rotational striking force is intermittently, repeatedly transmitted from the tip tool to the screw, whereupon the screw is driven into the material to be fastened, such as lumber.
Incidentally, in such an impact driver 1, air inlets 17 and air outlets 18 that supply and discharge cooling air are formed on either side of the body 5A of the housing 5. Cooling air is drawn into, by suction, the housing 5 by way of the air inlets 17 by means of a cooling fan 9 that rotates along with the output shaft 6 of the electric motor 3. Thus, the cooling air supplied into the housing 5 flows forwardly after passing by the electric motor 3, to thus cool the electric motor 3, and are subsequently discharged outside the housing 5 from the air outlets 18.
A plurality of slit-shaped ribs 17a are provided in the air inlet 17 formed in the housing 5, and a plurality of slit-shaped ribs 18a are also provided in the air outlets 18 formed in the housing 5. A contrivance is made, by means of the ribs 17a and 18a, to partition the air inlets 17 and the air outlets 18 into pores, thereby preventing intrusion of extraneous matter into the housing 5.
Although intrusion of extraneous matter, which are greater than the air inlets 17 partitioned into the pores by the ribs 17a, into the housing 5 is prevented, extraneous matter that is smaller than the air inlets 17 passes through the air inlets 17, to thus enter the housing 5 and adhere to the ball bearings 7 and 8 supporting the output shaft 6 of the electric motor 3 and induce anomalous rotation in the electric motor 3 as a result of depletion of grease of the ball bearings 7 and 8. Alternatively, extraneous matter is attracted by the magnetic force of a magnet 3a of the electric motor 3, to thus enter between an armature core 3b and the magnet 3a and induce a breakdown, such as deactivation of the electric motor 3. Such a problem easily takes place in a working environment where there is much extraneous matter, such as dust or metal powder.
JP-2003-200364-A describes a technique for closing a portion of an air outlet (an air exit port) by means of a cover in such a way that hot air resultant from cooling of the electric motor does not flow toward a face.
Japanese Patent No. 3674308 describes a technique for attaching a reclosable cover to an air vent; and causing the cover to operate to open the air vent during operation of a tool and close the air vent when the tool is at rest.
However, according to the technique described in connection with JP-2003-200364-A, only the portion of the air outlet (the air exit port) is closed by means of the cover. The air inlet still remains open, and intrusion of extraneous matter from the air inlet into the housing cannot be hindered, so that the problem attributable to intrusion of extraneous matter cannot be solved.
According to the technique described in connection with Japanese Patent No. 3674308, only the air vent is closed while the tool is at rest, and both an air intake and the air vent still remain open when the tool is in operation. Therefore, intrusion of extraneous matter into the housing cannot be hindered, and the problem attributable to intrusion of extraneous matter cannot be solved.